A browser application is client software used for retrieving, presenting, and traversing information resources on the Internet and other networks. When a browser is executed and establishes contact with a content source, for example an Internet site, the content source may choose a format for presentation of requested content based on the browser. The execution of the browser application may include activation of a user agent component that may be recognized and referred to by the content source in providing the requested content to the browser. The browser may specify hardware display capabilities or requirements of the requesting client device. The browser also may specify a communication point or port for receipt of the requested content. The browser and user agent communicate with content sources using the hypertext transfer protocol (HTTP). The content source may choose the presentation format to use in providing the requested content to the browser. If the content source has only a hypertext markup language (HTML) version of content available, this is the format of the content that the content source delivers. If the content source has multiple presentation formats available of the requested content, the content source may make an arbitrary choice of content to present based on the type of user agent involved in the browser session.